I made a test today: I assumed the couple bios/vbios don't know my native resolution (which makes sense regarding all the weird EDID values you all reported) and set an override resolution of 1440x900 (FYI my native resolution is 1280x800). The 1440x900 was shown in the ?video menu but with attr: 0xba . 0xba is a pair number, which basically means the mode is not supported.
Could you all check that if the mode is shown in the ?video list, the attr ends with a pair number or either a, c or e ?
Could you also try to set 1280x800, 1024x640 and 800x500?
Here is my guess : Standard VESA resolutions go from 320x240 up to 1280x1024. Therefore, the VESA implementation may decide not to report higher modes as valid, and therefore refuse to set such modes.
EDIT: Well, depends on the way it's implemented since some people can get higher resolution.
If I'm right, the highest mode available on wide-screens is 1280x800. And it makes the initial goal unreachable with this method.
PS: Thank you CEOS, but since I could predict the behaviour, this time, no output is required.